Mineral nutrition of sheep: new insights into interactions when grazing vegetative crops

addressing the need for mineral supplements for sheep grazing dual-purpose wheat (Dove 2007; Dove et al. 2007, 2012; Dove and McMullen 2009). Responses have been variable but overall assessment indicates there are positive growth responses to sodium (Na) and magnesium (Mg) supplements. The specific causes of the responses have not been easy to interpret due to a multiple mineral imbalance. The wheat plants are very low in Na (often 10–20 % of requirement) and marginal in Mg and calcium (Ca); the situation is further complicated by high potassium (K) (800–1000 % of requirement) (Dove and Kelman 2015b). The high K and low Na potentially reduce Mg absorption and the high Kmay also interfere with Ca metabolism by causing a high, positive dietary cation–anion difference (Masters and Thompson 2015). It is worthwhile examining these responses in more detail. In early experiments, significant liveweight responses (30–50%) were measured following supplementation with a mixed mineral supplement (containing Mg, Na and Ca) or to supplements tha